A hybrid automatic repeat request (HARQ) scheme will be described. The HARQ scheme is a combination of a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. According to the HARQ scheme, it is determined whether an unrecoverable error is included in data received by a physical layer, and retransmission is requested upon detecting the error, thereby improving performance.
A receiver using the HARQ scheme basically attempts error correction on the received data, and determines whether the data will be retransmitted or not by using an error detection code. Various codes can be used as the error detection code. For example, when using a cyclic redundancy check (CRC), upon detection of an error of the received data in a CRC detection process, the receiver transmits a non-acknowledgement (NACK) signal to a transmitter. Upon receiving the NACK signal, the transmitter transmits relevant retransmission data according to an HARQ mode. The receiver receives the retransmission data and then performs decoding by combining the retransmission data with previous data. As a result, reception performance is improved.
The HARQ mode can be classified into a chase combining mode and an incremental redundancy (IR) mode. In the chase combining mode, to obtain a signal-to-noise ratio (SNR), error-detected data is combined with retransmitted data instead of discarding the error-detected data. In the IR mode, additional redundant information is incrementally transmitted with retransmitted data to reduce an overhead resulted from retransmission and to obtain a coding gain.